Dan Stowell's VAMP plugin ported to web browsers as a WAM. This version runs as a PNaCl module so it requires Chrome. Blocksize is set to 256, which seems to work ok in OSX but I'm not sure if Windows is up to it. Blocksize can of course be defined larger at the expense of increased latency.
This is just a proof of concept. There's still plenty to do before the wrapper is generic enough.